I had a similar problem with my samba server. I fixed it by following the advice in the Samba Trouble Shooting Guide.
A firewall may be blocking net bios data between the machines. From a DOS prompt, try typing:
nbtstat -A ip (add the samba machine's IP address in place of ip).
If it doesn't list any shares, then port 137 is blocked. So you need to reconfigure the firewall to permit UDP traffic on ports 137 and 138, and TCP traffic on 139.
By the way, that trouble shooting guide is available at:
I found it to be a huge help when I was installing my samba server.
Hope this helps,